Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$146.35	6.261%	$155.513	$155.51	$155.50	$155.50
Purchase #2	$242.68	11.718%	$271.1172	$271.12	$271.10	$271.10
Purchase #3	$147.80	13.860%	$168.2851	$168.29	$168.30	$168.30
Purchase #4	$101.73	11.325%	$113.2509	$113.25	$113.25	$113.30
Purchase #5	$78.86	6.532%	$84.0111	$84.01	$84.00	$84.00
Purchase #6	$100.64	6.822%	$107.5057	$107.51	$107.50	$107.50
Purchase #7	$73.90	6.307%	$78.5609	$78.56	$78.55	$78.60
7 purchase totals =	$891.96		$978.2439	$978.25	$978.20	$978.30